The invention relates to a method and apparatus for the processing of dead animal material, such as offal.
Dead animal material, such as entrails and bones with residues of organic material, for example from slaughterhouses, but also complete carcasses are converted in an offal processing installation into, in the main, fat and meat bonemeal. The offal largely consists of water. The bulk of this has to be removed. In addition, the requirement is that the dead animal material is subjected to a sterilization treatment.
In general, an apparatus for the processing of offal comprises a first section in which the offal is preboiled and the mixture formed is then sterilized. The mixture pre-treated in this way is then fed to a second section in which the major portion of the water is evaporated. The fat and meat bonemeal are then separated off.
In the past, it was customery to carry out the first part of the processing process batch-wise.
However, there is a tendency also to carry out this first part of the offal processing process continuously and a screw press then provide for the separation into fat and solid substances.
However, this known system has the following disadvantages.
The sterilization takes place in a holding vessel. The residence time of the various particles of the material present in the vessel is thus different for each of the particles and not controllable. This means that in order to ensure that every particle obtains the required sterilization treatment, the mean residence time of the particles in the vessel is greater than the residence time required for one particle. In order to obtain a good sterilization, a particle must be kept at a temperature of 133.degree. C. for 20 minutes.
Furthermore, the system has the disadvantage that two pumps are needed to transport the material through the pre-drier and the sterilizer.
In order to obtain a readily pumpable substance, 1 kg of fat has to be supplied per 1 kg of offal and intermediate storage vessels provided with stirrer devices have to be used. As a result of the recirculation of the fat and as a consequence of the long storage time at high temperature, the content of free fatty acids in the fat will rise, which leads to an impairment in quality.
A further disadvantage is that during pre-drying, in which use is made of electrically/mechanically compressed waste vapours, the required heat transfer can be achieved only if the pumpable material contains very fine particles. The consequence of this is that the material is difficult to press, because of the lack of structure, on pressing at the end of the process. Moreover, a great deal of electrical energy is needed for the mechanical compression and for the fine comminution. With the known system the waste vapours emerging from the pre-boiler have reached a temperature of only about 125.degree. C. and then also have to be post-sterilized in an installation; this is also to be regarded as a disadvantage.